Ignition control for reformate engine

ABSTRACT

During operation of a spark ignition engine, an ignition system produces an output (e.g., breakdown voltage, peak secondary coil current, and spark duration) used to combust a charge (e.g., mixture of air and fuel) in an engine cylinder. Ignition output is important to consider in engines including a second fuel with high ignitability, for example in engines with a fuel reformer system. Example methods, devices and systems are included for adjusting ignition output.

TECHNICAL FIELD

The present application relates to ignition system output control in anengine including a second fuel with high ignitability, for example anengine with a reformer system to generate hydrogen-rich fuel.

BACKGROUND AND SUMMARY

During operation of a spark ignition engine, an ignition system producesan output (e.g., breakdown voltage, peak secondary coil current, andspark duration) used to initiate combustion of a charge (e.g., mixtureof air and fuel) in an engine cylinder. If the chemical and physicalproperties of a given charge have lower ignitability, ignition outputfor combustion is greater than an ignition output for another chargehaving higher ignitability. Engines including devices and systems, suchas a compressor providing boosted air, an exhaust gas recirculation(EGR) system, and variable valve control (VVC) systems controlling,e.g., timing, duration and lift, may all impact charge ignitability,leading to increased ignition system output requirements.

In one approach, an ignition system produces a modular output. Highignition output is used under some conditions, such as during light loadoperating conditions when spark duration may be increased. Further,during high load and/or high dilution conditions peak secondary currentand breakdown voltage may be increased.

The inventors herein have recognized issues with the above describedapproach. Parasitic efficiency losses are incurred when ignition outputis increased, partially cancelling the efficiency benefits of highdilution and/or boosted engines. Further, increasing the range ofignition output may drastically increase ignition systems cost. Furtherstill, without a wide range of ignition system output capabilities, anengine may not aggressively utilize lean burn, EGR, variable valvecontrol, boost, etc. while avoiding misfires, excessive spark plugelectrode erosion and the like.

Consequently, systems, devices and methods are disclosed for ignitioncontrol for an engine, such as a multi-fuel engine with a reformer forgenerating reformed fuel. In one example, a method for an engineincludes adjusting a spark duration of a spark plug included in anignition system, the spark plug coupled to a cylinder of the engine, theadjusting based on a reformate amount in a reformate storage tank. In afurther example, a method for an engine includes adjusting a chargereformate concentration in a cylinder of the engine, the engineincluding an ethanol-based fuel reformate system including a reformatecatalyst, the adjusting based on a spark duration of a spark plugincluded in an ignition system of the engine, the spark plug coupled tothe cylinder.

An engine including a fuel reformer system, e.g., an ethanol based fuelreformate system, may increase charge ignitability by increasingreformate, thus alleviating the use of increased ignition system output.Consequently, lean burn, EGR, boost, VVC (or similar systems such as camprofile switching (CPS), variable cam timing (VCT), variable valvetiming (VVT), variable valve lift (VVL), etc.) and the like may be moreaggressively utilized while reducing potential engine misfire. Forexample, when operating with an increased reformate amount, higher EGRlevels, and/or more retarded valve timing, may be used. Additionally,there is an unexpected synergy such that increased ignition output maybe used to conserve reformate.

It will be understood that the summary above is provided to introduce insimplified form a selection of concepts that are further described inthe detailed description, which follows. It is not meant to identify keyor essential features of the claimed subject matter, the scope of whichis defined by the claims that follow the detailed description. Further,the claimed subject matter is not limited to implementations that solveany disadvantages noted above or in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows engine systems.

FIG. 2 illustrates a higher level routine for operating an engine.

FIG. 3 illustrates an example routine for adjusting ignition outputbased on engine conditions.

FIG. 4 illustrates an example routine for adjusting at least one ofboost, dilution and charge reformate concentration based on ignitionoutput.

DETAILED DESCRIPTION

In the present application, an example engine including fuel systems anddevices for both liquid and gaseous fuel (e.g., hydrogen-rich reformate)is introduced and described with respect to FIG. 1. Next, a method forcontrolling such an engine in a first operating mode (e.g., adjustingignition output based on engine conditions) and a second operating mode(e.g., adjusting boost, dilution, and reformate amount based on ignitionoutput) is described with respect to FIG. 2. Further example methods forthe first and second operating modes are described with reference toFIGS. 3 and 4, respectively.

Referring to FIG. 1, internal combustion engine 10, includes a pluralityof cylinders, one cylinder of which is shown in FIG. 1. Internalcombustion engine 10 is controlled by electronic engine controller 12.Engine 10 includes combustion chamber 30 and cylinder walls 32 withpiston 36 positioned therein and connected to crankshaft 40. Combustionchamber 30 is shown communicating with intake manifold 44 and exhaustmanifold 48 via respective intake valve 52 and exhaust valve 54.

In this example, intake valve 52 and exhaust valves 54 may be controlledby cam actuation via respective cam actuation systems 51 and 53. Camactuation systems 51 and 53 may each include one or more cams and mayutilize one or more of cam profile switching (CPS), variable cam timing(VCT), variable valve timing (VVT) and/or variable valve lift (VVL)systems that may be operated by controller 12 to vary valve operation.The position of intake valve 52 and exhaust valve 54 may be determinedby position sensors 55 and 57, respectively. In alternative embodiments,intake valve 52 and/or exhaust valve 54 may be controlled by electricvalve actuation (EVA). For example, cylinder 30 may alternativelyinclude an intake valve controlled via electric valve actuation and anexhaust valve controlled via cam actuation including CPS and/or VCTsystems.

Intake manifold 44 is also shown coupled to the engine cylinder havingfuel injector 66 coupled thereto for delivering liquid fuel inproportion to the pulse width of signal FPW from controller 12. Fuel isdelivered to fuel injector 66 by a fuel system including fuel tank 91,fuel pump (not shown), fuel lines (not shown), and fuel rail (notshown). The engine 10 of FIG. 1 is configured such that the fuel isinjected directly into the engine cylinder, which is known to thoseskilled in the art as direct injection. Alternatively, liquid fuel maybe port injected. Fuel injector 66 is supplied operating current fromdriver 68 which responds to controller 12. In addition, intake manifold44 is shown communicating with optional electronic throttle 64. In oneexample, a low pressure direct injection system may be used, where fuelpressure can be raised to approximately 20-30 bar. Alternatively, a highpressure, dual stage, fuel system may be used to generate higher fuelpressures.

Gaseous fuel may be injected to intake manifold 44 by way of fuelinjector 89. In another embodiment, gaseous fuel may be directlyinjected into cylinder 30. One example of gaseous fuel is hydrogen-richreformate, such as generated from reforming ethanol, or anethanol/gasoline mixture, for example. Gaseous fuel is supplied to fuelinjector 89 from storage tank 93 by way of pump 96 and check valve 82.Pump 96 pressurizes gaseous fuel supplied from an onboard fuel reformer97 in storage tank 93. Check valve 82 limits flow of gaseous fuel fromstorage tank 93 to fuel reformer 97 when the output of pump 96 is at alower pressure than storage tank 93. Fuel reformer 97 includes catalyst72 and may further include optional electrical heater 98 for reformingliquid fuel (e.g., an alcohol, ethanol, methanol, or mixture thereof)supplied from fuel tank 91. Fuel reformer 97 is shown coupled to theexhaust system downstream of catalyst 70 and exhaust manifold 48.However, fuel reformer 97 may be coupled to exhaust manifold 48 andlocated upstream of catalyst 70. Fuel reformer 97 may use exhaust heatto drive an endothermic dehydrogenation of alcohol supplied by fuel tank91 and to promote fuel reformation.

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 48 upstream of catalytic converter 70. Alternatively, atwo-state exhaust gas oxygen sensor may be substituted for UEGO sensor126.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst inone example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106, random access memory 108, keep alive memory 110, and aconventional data bus. Controller 12 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a position sensor134 coupled to an accelerator pedal 130 for sensing force applied byfoot 132; a measurement of engine manifold pressure (MAP) from pressuresensor 122 coupled to intake manifold 44; an engine position sensor froma Hall effect sensor 118 sensing crankshaft 40 position; a measurementof reformer tank pressure from pressure sensor 85; a measurement ofreformer tank temperature from temperature sensor 87; a measurement ofair mass entering the engine from sensor 120; and a measurement ofthrottle position from sensor 62. Barometric pressure may also be sensed(sensor not shown) for processing by controller 12.

In a preferred aspect of the present description, engine position sensor118 produces a predetermined number of equally spaced pulses everyrevolution of the crankshaft from which engine speed (RPM) can bedetermined. In one embodiment, the stop/start crank position sensor hasboth zero speed and bi-directional capability. In some applications abi-directional Hall sensor may be used, in others the magnets may bemounted to the target. Magnets may be placed on the target and the“missing tooth gap” can potentially be eliminated if the sensor iscapable of detecting a change in signal amplitude (e.g., use a strongeror weaker magnet to locate a specific position on the wheel). Further,using a bi-dir Hall sensor or equivalent, the engine position may bemaintained through shut-down, but during re-start alternative strategymay be used to assure that the engine is rotating in a forwarddirection.

In some embodiments, the engine may be coupled to an electricmotor/battery system in a hybrid vehicle. The hybrid vehicle may have aparallel configuration, series configuration, or variation orcombinations thereof.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 44, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g. whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC). During thecompression stroke, intake valve 52 and exhaust valve 54 are closed.Piston 36 moves toward the cylinder head so as to compress the airwithin combustion chamber 30. The point at which piston 36 is at the endof its stroke and closest to the cylinder head (e.g. when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top dead center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by known ignition means such as spark plug 92, resultingin combustion. During the expansion stroke, the expanding gases pushpiston 36 back to BDC. Crankshaft 40 converts piston movement into arotational torque of the rotary shaft. Finally, during the exhauststroke, the exhaust valve 54 opens to release the combusted air-fuelmixture to exhaust manifold 48 and the piston returns to TDC. Note thatthe above is shown merely as an example, and that intake and exhaustvalve opening and/or closing timings may vary, such as to providepositive or negative valve overlap, late intake valve closing, orvarious other examples.

Turning now to FIG. 2, a higher level routine 200 is shown, foroperating an example engine (such as engine 10 described above withrespect to FIG. 1). Routine 200 is one example of a method for operatingignition output, dilution, boost and reformate amount (such as theamount of reformate in the charge inducted into the cylinder, chargereformate concentration) in the example engine. In the present example,the engine includes a gaseous fuel that is a hydrogen-rich reformate.

Routine 200 begins at 210 by measuring or inferring current engineconditions and ignition output. Engine conditions include an enginespeed, an engine load, a pressure inside one or more cylinders, FPW (forliquid and gaseous fuels), various charge motion properties (such ascharge velocity, swirl, and tumble), charge dilution (e.g., due to leanburn, VVC, and EGR), and a volume of reformate in an example storagetank (e.g., a reformate amount). The charge motion may be based on aposition of a charge motion control valve coupled in the engine intakeport. Further, ignition output controls spark energy in an example sparkplug. Ignition output may be characterized by parameters including abreakdown voltage between terminals of the spark plug, a peak currentrunning through a secondary coil electrically coupled to the spark plugand a spark duration in the spark plug. In alternate examples, sparkduration may be determined for each of a number of quickly succeedingspark discharges, and may be augmented by a parameter determining thenumber of sparks across the spark plug during a given four stroke cycle.

After 210, the routine includes determining if ignition output should beadjusted in response to engine conditions at 212. In one example, 212includes determining if a reformate amount in a storage tank of theexample engine is above a transition threshold. If the amount is belowthe transition threshold, the routine continues to 214 to adjustignition output in response to engine conditions; otherwise routine 200continues to 216 to adjust at least one of boost, dilution and chargereformate concentration in response to ignition output. In the presentexample, one advantage is that a certain amount of reformate isavailable for use to control charge ignitability in a combustion chamberby increasing the total amount of fuel in the charge and/or increasingthe percentage of fuel in the charge that is reformate. In this way,charge reformate concentration alters charge ignitability in additionto, or in place of, adjusting ignition output based on chargeignitability (e.g., increasing spark duration).

Additionally, routine 200 may include hysteresis. For example, duringmeasuring or inferring of current engine conditions and ignition outputincluded at 210, the routine may include measuring if the engine is orhas recently adjusted ignition output in response to engine conditions(e.g., first mode included at 214) or adjusted at least one of boost,dilution and charge reformate concentration in response to ignitionoutput (e.g., second mode included at 216). Depending on if the engineis operating in the first or second mode, the valve of a transitionthreshold included at 212 may increase or decrease. One advantage ofsuch a variable transition threshold is that an increase in reformateproduction may be ensured before increasing reformate use, or converselythat reformate is used effectively to limit adjusting ignition outputadjusting/modulation.

In an additional example, 212 may include determining if the engine isin a performance mode or not. A performance mode may include a demandedtorque above a demanded torque threshold, or a performance flagactivated, for example, by user toggling a user input or switch. In onesuch example, if the engine is in a performance mode, the routine 200continues to 214, otherwise, the routine continues to 216. In furtherexamples, 212 includes additional determinations of whether to adjustignition output in response to engine conditions, such as if a currentcharge is ignitable given current ignition output and engine conditions,or if an engine system is in a limited engine output operating mode.

Returning now to routine 200, if at 212 ignition output is to beadjusted in response to engine conditions, routine 200 may continue to214. 214 includes a first engine operating mode, adjusting ignitionoutput in response to engine conditions. 214 may further includeadjusting (e.g., increasing) spark duration in response to the reformateamount below a first reformate threshold. The first reformate thresholdmay be the same or different from the transition threshold. One exampleof the first operating mode is described below with respect to routine300 illustrated in FIG. 3. After 214, routine 200 may end.

If, at 212, ignition output is not to be adjusted in response to engineconditions, routine 200 may continue to 216. 216 includes a secondengine operating mode, adjusting at least one of boost, dilution, andcharge reformate concentration in response to ignition output. In oneexample, 216 includes increasing a charge reformate concentration in thecylinder of the engine in response to the spark duration less than aduration threshold. In a further example, 216 includes decreasing chargereformate concentration in response to the reformate amount less than asecond reformate threshold (described in more detail below).Additionally, routine 400 described below with respect to FIG. 4 is oneexample of the second operating mode. After 216, routine 200 may end.

Turning now to FIG. 3, an example routine 300 is shown. Routine 300 isone example of a method for adjusting ignition output based on engineconditions in an example engine. The example engine includes a fuelreformer system, including catalyst, tank for storing gaseous fuel,etc., as described above with respect to FIG. 1. Adjusting ignitionoutput includes increasing or decreasing breakdown voltage, peaksecondary current, spark duration, number of sparks, and/or combinationsthereof. Routine 300 may be a subroutine incorporated into a higherlevel routine (e.g., at 214 of routine 200, described above) or may berun independently. Further, routine 300 may be run in multipleiterations for continuous control of ignition output in response toengine conditions.

In the present example, routine 300 begins at 310 by determining if apressure level in a cylinder of the engine is greater than a pressurethreshold. In some examples routine 300 begins by measuring or inferringcurrent engine conditions, e.g., 210 included in routine 200, describedabove. However, if routine 300 is a subroutine of a higher levelroutine, such as routine 200, measuring or inferring current engineconditions may be omitted, as shown in the present example. Sensorreadings and measurements, such as described above with respect to FIG.1, include UEGO, valve lift, valve timing, engine speed, MAP, FPW (forliquid and gaseous fuels), and air mass entering an intake. Further,sensor readings and measurements may be combined with static physicalconstants such as dimensions of a combustion chamber of the engine,physical constants for partial pressures of gaseous and liquidchemicals, etc. to calculate, for example, a cylinder pressure.

Returning to routine 300, at 310 cylinder pressure is compared to apressure threshold. The pressure threshold may be a fixed valuethreshold, or may be variable depending on measured engine conditions.For example, the threshold may be a function of engine speed-load,dilution, and/or charge reformate concentration. The threshold value maybe stored in a look up table or other standard method known to oneskilled in the art.

If the cylinder pressure is greater than a pressure threshold, routine300 continues to 312. In this way routine 300 includes one example ofincreasing at least one of a breakdown voltage and a peak secondarycurrent in the spark plug in response to a cylinder pressure above acylinder pressure threshold.

In the present example, 312 includes igniting with a first breakdownvoltage and first peak current. Additional examples include separate, orindependent, control of breakdown voltage and peak current, e.g.,igniting with only one of the first breakdown voltage or the first peakcurrent based on operating conditions. For example, during, or inresponse to, high engine loads and/or when spark is retarded, increasedvoltage may be used; however, in some examples, a decreased current maybe sufficient. Similarly, during, or in response to, high engine speedsand/or when charge motion is higher, increased peak secondary currentmay be used; however, in some examples, a decreased breakdown voltagemay be sufficient.

In the present example, the second voltage is less than the firstvoltage and the second current is less than the first current. Further,312 may include setting one or more flags to ignite with a firstbreakdown voltage and/or a first peak current during the next ignitionevent. In some examples, routine 300 ends after 312.

In additional examples of routine 300, 312 includes incrementing atleast one of breakdown voltage and peak current by a discrete voltageinterval or a discrete current interval. Still further examples ofroutine 300 include proportionally increasing one or both of voltage andcurrent. The increase may be proportional to cylinder pressure, and/orcharge motion, for example. After 312, routine 300 continues to 318,described in more detail below.

If the cylinder pressure is not greater than a pressure threshold at310, routine 300 continues to 314. Additionally, in further examples ofroutine 300, 314 may be run in parallel with 310 or done before 310. 314includes determining if charge motion is greater than a charge motionthreshold. Charge motion includes the motion with which gases move froman example intake manifold to an example combustion chamber, as well asvortex motion of these gases inside the combustion chamber (e.g., tumbleand swirl). Charge motion may be inferred based on, for example, valvelift, valve opening timing and duration, valve overlap, MAP, chargemotion control valve position, or others. If charge motion is greaterthan the charge motion threshold, then the routine may continue to 312,described above. In this way routine 300 includes one example ofincreasing at least one of a breakdown voltage and a peak secondarycurrent in the spark plug in response to a charge motion above a chargemotion threshold.

If charge motion is less than the charge motion threshold, then theroutine may continue to 316. 316 includes igniting with the secondvoltage value and second current value. Further, 316 may include settingone or more flags to ignite with the second breakdown voltage and/or thesecond peak current during the next ignition event. In some examples,routine 300 ends after 316.

In additional examples of routine 300, 316 includes decrementing atleast one of breakdown voltage and peak current by a discrete voltageinterval or a discrete current interval. Still further examples ofroutine 300 include proportionally decreasing one or both of voltage andcurrent. The decrease may be proportional to cylinder pressure, and/orcharge motion, for example. After 316, routine 300 continues to 318,described in more detail below.

Continuing with routine 300, after 316 or 312, the routine continues to318, which includes determining if an engine speed-load is less than aspeed-load threshold. In some examples, speed-load may be inferred fromengine speed, cylinder pressure in one or more cylinders, torque anddemanded torque. The speed-load threshold may be static or dynamic,similar to the pressure threshold included at 310, and the charge motionthreshold at 314, both described above.

If the engine speed-load is below the speed-load threshold, the routine300 continues to 324. 324 includes igniting with a first spark duration.In additional examples, 324 may include setting one or more flags thatindicate that a first spark duration should be used during the nextignition event. As discussed above with respect to 312, additionalexamples of routine 300 include incrementing spark duration by adiscrete time interval at 324. Still further examples of routine 300include increasing spark duration in proportion to engine speed-load,charge dilution and charge reformate concentration. After 324, routine300 may end.

Routine 300 includes one example of increasing spark duration inresponse to an engine speed-load above a speed-load threshold (e.g., at318 and 324). If the engine speed-load is not below the speed-loadthreshold at 318, the routine 300 continues to 320. 320 includesdetermining if a charge dilution is above a first dilution threshold.Charge dilution may include a percent EGR in the intake charge (relativeto fresh air), for example. The first dilution threshold may be staticor dynamic, similar to the pressure threshold included at 310, and thecharge motion threshold at 314, both described above.

In the present example, if charge dilution is above the first dilutionthreshold, routine 300 continues to 324, described above. In this way,routine 300 includes one example of increasing spark duration inresponse to a charge dilution above a dilution threshold.

If charge dilution is not above the first dilution threshold, routine300 continues to 322 which includes determining if a reformate amount isbelow a first reformate threshold. Reformate may be is stored an examplestorage tank. Determining reformate amount may be inferred from a tankpressure, or a flow rate out of the tank.

If the reformate amount is less than the first reformate threshold, theroutine 300 continues to 324. In this way, routine 300 includes oneexample of increasing spark duration in response to the reformate amountbelow a reformate threshold.

If the reformate amount is not less than the first reformate threshold,the routine 300 continues to 326, igniting with a second spark durationless than the first spark duration. In additional examples of routine300, 326 may include setting one or more flags to ignite with the secondspark duration during the next ignition event. Further, 326 may includedecrementing spark duration by a discrete time interval. Still furtherexamples of routine 300, include proportionally decreasing sparkduration at 326. The decrease may be proportional to speed-load, chargedilution, and reformate amount.

Further still, this is one example of decreasing spark duration inresponse to the reformate amount below the reformate threshold.Furthermore, 326 may include increasing charge reformate concentration.This is one example of how routine 300 includes increasing chargereformate concentration in response to the reformate amount above thereformate threshold. After 326, the routine may end.

Determining, at 322, if reformate is below a first reformate thresholdand then igniting with either a first or second spark duration is oneexample of adjusting spark duration of an example spark plug included inan ignition system, the adjusting based on a reformate amount in areformate storage tank. Further routines and methods include additionalexamples.

Routine 300 is one example of a routine for adjusting ignition outputbased on engine conditions. Because ignition output is modulated (e.g.,spark duration is increased or decreased, etc.), reformate usage may bereduced. Further, aggressive use of lean burn, EGR, and the like may besustained by modulating ignition output according to routine 300.

Turning now to FIG. 4, an example routine 400 is shown. Routine 400 isone example of a method for adjusting at least one of boost, dilution,and charge reformate concentration based on conditions in an exampleengine (e.g., ignition output). The present example engine includes anignition system, a fuel reformer system, including catalyst, tank forstoring gaseous fuel, etc., as described above with respect to FIG. 1.More specifically, routine 400 includes determinations based on engineconditions and conditions of one example combustion chamber of anexample engine cylinder, an example spark plug coupled to the cylinder.Routine 400 may be a subroutine incorporated into a higher level routine(e.g., at 216 of routine 200, described above) or may be runindependently. Further, routine 400 may be run repeatedly for continuouscontrol of at least one of boost, dilution and charge reformateconcentration based on ignition output.

In the present example, routine 400 begins at 410 by determining ifignition of an example charge in a cylinder is capable. In some examplesroutine 400 begins by measuring or inferring current engine conditions,e.g., 210 included in routine 200, described above. However, if routine400 is a subroutine of a higher level routine, such as routine 200,measuring or inferring current engine conditions may be omitted, asshown in the present example. Sensor readings and measurements, such asdescribed above with respect to FIG. 1, include UEGO, valve lift, valvetiming, engine speed, MAP, FPW (for liquid and gaseous fuels), and airmass entering an intake. Further, sensor readings and measurements maybe combined with static physical constants such as dimensions of acombustion chamber of the engine, physical constants for partialpressures of gaseous and liquid chemicals, etc. to calculate, forexample, a cylinder pressure.

Returning to 410, determining if ignition is capable may be inferred by,for example, breakdown voltage, peak secondary current, spark duration,FPW (for liquid and gaseous fuels), valve lift, valve opening duration,valve overlap, MAP, air mass, and UEGO. In one example, the routine maydetermine whether potential for engine misfire due to insufficientignition energy is above a threshold for the current operatingconditions. If ignition is capable, then the routine 400 may end. Ifignition is not capable, routine 400 continues to 412.

At 412, routine 400 includes determining if a reformate amount is abovea second reformate threshold. The second reformate threshold may bedifferent than an example first reformate threshold (described abovewith reference to routine 300) and an example transition threshold(described above with references to routine 200); for example the secondthreshold may be less than both an example first reformate threshold andan example transition threshold. If the reformate amount is not greaterthe second threshold, routine 400 continues to 418.

In further examples of routine 400, a charge reformate concentration isdecreased before routine 400 continues from 412 to 418. In this wayroutine 400 may include decreasing charge reformate concentration inresponse to a reformate amount less than a second reformate threshold.

In the present example, if the reformate amount is greater than thesecond reformate threshold, routine 400 continues to 414 to determine ifspark duration in an example combustion chamber is less than a durationthreshold. If spark duration is less than the duration threshold,routine 400 continues to 416 to increase charge reformate concentration.In further examples of routine 400, 414 includes determining at leastone of if a breakdown voltage is below a breakdown threshold and if apeak secondary current is below a current threshold.

Increasing charge reformate concentration at 416 includes using a firstcharge reformate concentration greater than a second charge reformateconcentration. In additional examples, 416 may include setting one ormore flags that indicate that a first charge reformate concentration isused during the next ignition event (e.g., the immediately followingignition event in a given cylinder). Additional examples of routine 400include incrementing charge reformate concentration by a discrete amountat 416. Still further examples of routine 400 include increasing chargereformate concentration in proportion to engine breakdown voltage, peaksecondary current and/or spark duration. After 416, the routine may end.In further examples of routine 400, after 416 the routine may continueto 418.

Determining if spark duration is less than the duration threshold (e.g.,at 414) and increasing charge reformate concentration in response (e.g.,at 416) is one example of adjusting a charge reformate concentration inthe cylinder of the example engine, the adjusting based on a sparkduration of an example spark plug.

Continuing with routine 400, at 418, the routine includes determining ifa charge dilution is greater than a second dilution threshold. Thesecond dilution threshold may be different than an example firstdilution threshold (described above with reference to routine 300); forexample the second dilution threshold may be less than the example firstdilution threshold. The second dilution threshold may be static ordynamic. If the charge dilution amount is not greater than the secondthreshold, routine 400 continues to 424. In further examples of routine400, a charge dilution is increased before routine 400 continues from418 to 424. In this way routine 400 may include increasing chargedilution in response to a charge dilution not greater than the seconddilution threshold.

In the present example, if the charge dilution is greater than thesecond dilution threshold, routine 400 continues to 420 to determine ifa breakdown voltage is less than a voltage threshold. If breakdownvoltage is less than the voltage threshold, routine 400 continues to 422to decrease dilution. In further examples of routine 400, 420 includesdetermining at least one of if a spark duration is below a durationthreshold, and if a peak secondary current is below a current threshold.

Decreasing dilution at 422 includes using a second dilution less than afirst dilution. In additional examples, 422 may include setting one ormore flags that indicate that a second dilution should be used duringthe next ignition event. Additional examples of routine 400 includedecrementing dilution by a discrete amount at 422. Still furtherexamples of routine 400 include decreasing dilution in proportion toengine breakdown voltage, peak secondary current and/or spark duration.After 422, the routine may end. In further examples of routine 400,after 422, the routine continues to 424.

Determining if charge dilution is less than the dilution threshold(e.g., at 418) and decreasing dilution in response (e.g., at 422) is oneexample of decreasing dilution in response to at least one of a sparkduration below a spark duration threshold, a spark voltage below avoltage threshold and a peak current below a current threshold.

If breakdown voltage is not less than a voltage threshold at 420, thenroutine 400 continues to 424. 424 includes determining if a boost amountis greater than a boost threshold. The boost threshold may be static ordynamic. If boost is not greater the boost threshold, routine 400 mayend. In further examples of routine 400, a boost amount is increasedafter 424 and before routine 400 ends. In this way routine 400 mayinclude increasing boost in response to boost not greater than the boostthreshold.

In the present example, if the boost is greater than the boostthreshold, routine 400 continues to 426 to determine if peak current isless than a current threshold. If peak current is less than the currentthreshold, routine 400 continues to 428 to decrease boost. In furtherexamples of routine 400, 426 includes determining at least one of if aspark duration is below a duration threshold, and if a breakdown voltageis below a voltage threshold. If peak current is not less than thecurrent threshold, routine 400 may end.

Decreasing boost at 428 includes using a second boost amount less than afirst boost amount. In additional examples, 428 may include setting oneor more flags that indicate that the second boost amount should be usedduring the next ignition event. Additional examples of routine 400include decrementing boost by a discrete amount at 428. Still furtherexamples of routine 400 include decreasing boost in proportion to enginebreakdown voltage, peak secondary current and/or spark duration. After428, the routine may end.

Determining if boost is less than the boost threshold (e.g., at 424) anddecreasing dilution in response (e.g., at 428) is one example ofdecreasing boost in response to at least one of a spark duration below aspark duration threshold, a breakdown voltage below a voltage thresholdand a peak secondary current below a current threshold.

The present example of routine 400 is only one example of a routine foradjusting at least one of boost, dilution and charge reformateconcentration based on ignition output. In the present example,adjusting spark duration in response to spark duration occurs beforeadjusting breakdown voltage and/or peak current in response to chargedilution. In turn, adjusting breakdown voltage and/or peak current inresponse to charge dilution occurs before adjusting peak current and/orbreak down voltage in response to boost. In further examples, each ofthese three processes may be done in parallel, or may be ordereddifferently.

In this way, parasitic efficiency losses and spark plug erosion may belessened because ignition output is lessened under some runningconditions. Further, ignition output range may be lessened, decreasingignition systems costs while still operating over wide range of engineconditions, such as during aggressive use of lean burn, EGR, variablevalve control, and boost and avoiding misfires, excessive spark plugelectrode erosion and the like.

It will be understood that the example control and estimation routinesdisclosed herein may be used with various system configurations. Theseroutines may represent one or more different processing strategies suchas event-driven, interrupt-driven, multi-tasking, multi-threading, andthe like. As such, the disclosed process steps (operations, functions,and/or acts) may represent code to be programmed into computer readablestorage medium in an electronic control system. It will be understoodthat some of the process steps described and/or illustrated herein mayin some embodiments be omitted without departing from the scope of thisdisclosure. Likewise, the indicated sequence of the process steps maynot always be required to achieve the intended results, but is providedfor ease of illustration and description. One or more of the illustratedactions, functions, or operations may be performed repeatedly, dependingon the particular strategy being used.

Finally, it will be understood that the articles, systems and methodsdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are contemplated. Accordingly, the presentdisclosure includes all novel and non-obvious combinations andsub-combinations of the various systems and methods disclosed herein, aswell as any and all equivalents thereof.

1. A method for an engine and a fuel reformer, the method comprising:adjusting a spark duration of a spark plug included in an ignitionsystem, the spark plug coupled to a cylinder of the engine, theadjusting based on a reformate amount in a storage tank.
 2. The methodof claim 1, wherein the tank is coupled to the fuel reformer, the methodfurther comprising increasing spark duration in response to thereformate amount below a reformate threshold, and decreasing sparkduration in response to the reformate amount above the reformatethreshold, the method further comprising decreasing reformateconcentration in the cylinder in response to the reformate amount belowthe reformate threshold.
 3. The method of claim 1, further comprisingincreasing at least one of a breakdown voltage and a peak secondarycurrent in the spark plug in response to a charge motion above a chargemotion threshold.
 4. The method of claim 1, further comprisingincreasing at least one of a breakdown voltage and a peak secondarycurrent in the spark plug in response to a cylinder pressure above acylinder pressure threshold.
 5. The method of claim 1, furthercomprising increasing spark duration in response to an engine speed-loadbelow a speed-load threshold.
 6. The method of claim 1, furthercomprising increasing spark duration in response to a charge dilutionabove a dilution threshold.
 7. The method of claim 1, where thereformate amount is produced by an onboard reformer.
 8. A method for anengine, the method comprising: adjusting a reformate amount in acylinder of the engine, the engine coupled to a fuel reformer system,the adjusting based on a spark duration of a spark plug included in anignition system of the engine, the spark plug coupled to the cylinder;and increasing charge reformate concentration in response to the sparkduration below a spark duration threshold; and increasing chargereformate concentration in response to at least one of a breakdownvoltage below a breakdown threshold and a peak secondary current below acurrent threshold.
 9. The method of claim 8, further comprising,decreasing a percent of EGR in an intake charge relative to fresh air inresponse to at least one of the spark duration below the spark durationthreshold, a spark voltage below a voltage threshold and the secondarypeak current below the current threshold.
 10. The method of claim 8,further comprising decreasing boost in response to at least one of thespark duration below the spark duration threshold, the breakdown voltagebelow the breakdown threshold and the peak secondary current below thecurrent threshold.
 11. A method for an engine comprising: in a firstmode, increasing a spark duration of a spark plug coupled to an enginecylinder in response to a reformate amount in a storage tank below afirst reformate threshold; and in a second mode different from thefirst, increasing a charge reformate concentration in the cylinder inresponse to the spark duration shorter than a duration threshold. 12.The method of claim 11, where the first mode further includes decreasingspark duration in response to the reformate amount above the reformatethreshold.
 13. The method of claim 11, where the second mode furtherincludes decreasing charge reformate concentration in response to aspark duration at or longer than the duration threshold.
 14. The methodof claim 11, further comprising transitioning from the first mode to thesecond mode in response a reformate amount above a transition threshold.15. The method of claim 11, further comprising transitioning from thesecond mode to the first mode in response to a reformate amount below atransition threshold.
 16. The method of claim 11, where the first modefurther includes increasing at least one of spark voltage and peakcurrent in a spark plug in response to at least one of a charge motionabove a charge motion threshold and a cylinder pressure above a cylinderpressure threshold.
 17. The method of claim 11, where the first modefurther includes increasing a spark duration in response to at least oneof an engine speed-load below a speed-load threshold and a chargedilution above a dilution threshold.
 18. The method of claim 11, wherethe second mode further includes decreasing boost in response to atleast one of a spark duration below a spark duration threshold, a sparkvoltage below a voltage threshold and a peak current below a currentthreshold.